BR112016007331B1 - use of a particulate carbon material - Google Patents

Abstract

USE OF A MICRODOMINIUM CARBON MATERIAL FOR THERMAL INSULATION. The present invention relates to the use of a particulate carbon material that comprises carbon particles in the shape of discs and hollow open cones in thermal insulation applications.

Description

[0001] The present invention relates to the use of a particulate microstructured carbon material in thermal insulation applications, preferably as an athermic charge.

[0002] Thermal insulation to save energy has reached great prominence in the context of the desire for sustainable development and the rising cost of energy. Thermal insulation is gaining more and more importance in the light of rising energy costs, increasingly scarce resources, the desire to reduce CO2 emissions, the need for a sustainable reduction in energy demand and also the increasingly demanding requirements that protection against heat and cold will have to meet in the future. These increasingly demanding requirements for optimizing thermal insulation apply equally to buildings, for example, new buildings or existing buildings, and for thermal insulation in the mobile, logistical and stationary sectors.

[0003] Building materials such as steel, concrete, masonry and glass, as well as natural rock, are relatively good thermal conductors so that the exterior walls of buildings produced from them release heat very quickly from the inside out in a cold climate . Therefore, the development aims, first, to improve the insulation properties by increasing the porosity of these construction materials as in the case of, for example, concrete and masonry and, secondly, to coat the external walls with thermal insulation materials. The thermal insulation materials that are most used in the present invention are materials that have a low thermal conductivity. The materials used include both organic and inorganic insulation materials, for example, foamed plastics such as polystyrene and polyurethane; wood fiber materials such as wood straw and cork; vegetable or animal fibers such as hemp, linen, wool; glass and mineral wool, plate-shaped foamed glass; calcium silicate sheets and plasterboard sheets. These thermal insulation materials are mostly used in the form of moldings and foamed or pressed plates, alone or in combination with others. Another effective way of providing thermal insulation is the use of vacuum insulated panels (VIPs) that are based on the vacuum insulation principle. These VIPs comprise a porous core material to support the vacuum and are surrounded by a highly gas-proof cover material. Materials that can be used for the core include open cell polymer foams, microfiber materials, fumed silica and perlite.

[0004] The insulating capacity of each of the aforementioned materials and the material / vacuum combinations, respectively, can be further improved by adding an athermic material capable of interacting with infrared radiation and, thus, reducing infrared transmission. . For example, athermic materials can be used as fillers in thermo-insulating polymeric foams and vacuum-insulated panels. Expandable thermoplastic polymers and among these, in particular, expandable polystyrene (EPS), are conventional insulation materials that have been known and used for a long time to prepare expanded articles that can be adopted in various areas of application, among which, a of the most important is thermal insulation. The flat sheets of expanded polystyrene are normally used with a density of about 30 g / l since the thermal conductivity of the polymer has a minimum of these values. It is not advantageous to go below this limit, even if this is technically possible, since this causes a drastic increase in the thermal conductivity of the sheet which must be compensated by an increase in its thickness. In order to avoid this disadvantage, the polymer can be filled with athermic materials such as graphite (for example, in Neopor® available from BASF), carbon black or aluminum. A good performance of the thermal load and, thus, of the complete thermal insulation allows a significant reduction in the density of the expanded article or the thickness of it without reducing the value of thermal resistance completely.

[0005] EP 620.246 A describes a process for preparing expandable polystyrene granules containing an athermic material, for example, carbon black, distributed on the surface or, alternatively, incorporated within the particle itself.

[0006] The use of carbon black has been known as a filler or pigment, or as a nucleating agent (see, for example, Chem. Abstr., 1987, "Carbon Black Containing Polystyrene Beads"). Among the various types of carbon black, the most important are carbon black from oil combustion ("oil carbon black"), carbon black from gas combustion, carbon black from acetylene, carbon black lamp smoke, channel carbon black, thermal carbon black and electrically conductive carbon black. WO 1997/45477 describes compositions based on expandable polystyrene comprising a polymer of styrene and from 0.05 to 25% of carbon black of the lamp carbon black type.

[0007] Depending on the manufacturing process, these carbon blacks have diameters ranging from approximately 10 nm to 1,000 nm, and have very different specific surfaces (from 10 to 2,000 m2 / g). These differences lead to different blocking capabilities than infrared rays. WO 2006/61571 describes compositions based on expandable polystyrene comprising a polymer of styrene and from 0.05 to less than 1% carbon black, with a surface area ranging from 550 to 1,600 m2 / g.

[0008] It is known that graphite can also be used effectively as a blackbody (as described, for example, in JP 63-183941, WO 04/022636, WO 96/34039). Its use as an attenuation agent for infrared radiation in polymeric foams is, however, more recent. Patent Application in JP 63183941 is among the first to propose the use of some additives, active in blocking infrared rays at wavelengths ranging from 6 to 14 μm and, therefore, obtaining insulating thermoplastic resins capable of permanently sustain low thermal conductivity. Among all additives, graphite is preferred.

[0009] DE 9305431 U describes a method for producing expanded molded products that have a density of less than 20 kg / m3 and a reduced thermal conductivity. This result is achieved by incorporating an athermic material, such as graphite and also carbon black, in the rigid polystyrene foam. The International Patent Application in WO 98/51735 describes expandable polystyrene particulates that contain from 0.05 to 25% by weight of particles of natural or synthetic graphite, homogeneously distributed in the polystyrene matrix. Graphite preferably has an average diameter ranging from 1 to 50 μm, an apparent density ranging from 100 to 500 g / l and a surface area ranging from 5 to 20 m2 / g.

[00010] WO 2011/042800 is directed to an expandable thermoplastic nanocomposite polymeric composition, preferably a polystyrene composition, which includes an athermic filler comprising nanoscale graphene sheets that have a thickness not exceeding 150 μm, an average dimension (length, width or diameter) not exceeding 10 μm and a surface area> 50 m2 / g.

[00011] There is a continuing need for highly effective insulation materials that have low space requirements and thus allow for multiple fields of use. The problem underlying the present invention is to find a particulate material that has exceptionally low radioactive conductivity that can be used in combination with conventional materials to improve thermal insulation. More particularly, an endogenous filler material is sought for use in polymeric foams and vacuum insulated panels.

[00012] It has been found that a particulate carbon material comprising disc-shaped carbon particles ("carbon discs") and hollow open cones ("carbon cones") can be used for thermal insulation.

[00013] The terms "carbon cones" and "carbon disks" are used to designate a certain class of carbon structures in the microdomain or smaller (nanodomain). These structures can be roughly described as stacks of graphical sheets with flat or conical structures. Open carbon cones are generally hollow, each made from a continuous sheet of graphite, except at its open edges. All cones are closed at the apex and only exist with five different opening angles. A graphical sheet composed of hexagons cannot only form a continuous cone cover, but forms a flat plate or disc. Pentagons have to be added to form a curved tip. The open carbon cones can be shaped like a wrapped graph sheet. In order to have seamless deformation-free wrapping, a sector has to be cut from the sheet and subsequently the edges have to be connected. Considering the symmetry of a graphite sheet, this sector must have an angle (= total declination TD) of TD = N x 60 °, where N = 0, 1, 2, 3, 4 or 5 and corresponds to the number pentagons needed to produce the particular total declination (curvature). Therefore, the opening angles α of the cones have only certain discrete values according to the equation α = 2 arcsen (1 - N / 6). A total declination of 0 ° (N = 0) corresponds to a flat plate, that is, the carbon discs can be described as flat circular graphite sheets that have only hexagonal graphite structure. Figure 1, taken from the International Application in WO 98/42621, shows schematically the projected angles (apex or opening angles) of the various possible carbon cones.

[00014] The concept of declination and angle projected as applied to carbon cones and disks is best understood in reference to the article "Graphitic Cones and the Nucleation of Curved Carbon Surfaces" that appears in Nature (1997), July 31st edition. As shown in Figure 1, the projected angles for each of the possible cones are 19.2 °, 38.9 °, 60 °, 83.6 ° and 112.9 °, which correspond to the total declines of 300 ° (N = 5), 240 ° (N = 4), 180 ° (N = 3), 120 ° (N = 2) and 60 ° (N = 1), respectively. In addition, flat sheet graphitic sheet has a projected angle of 180 ° and a total declination of 0 °. Electromicrographs of the particulate carbon material confirm the presence of discs and cones that have at least one of the opening angles mentioned above. Carbon cones that have different opening angles than those mentioned have not been observed.

[00015] The characteristic size, or longest dimension, of carbon cones and discs is typically less than 5 μm, preferably less than 4 μm, more preferably not more than 2 μm such as 1 to 2 μm or less than 1 μm or less than 800 nm, and the thickness, measured as the wall thickness of hollow open carbon cones or the thickness of the discs, is typically less than 100 nm, preferably less than 80 nm, more preferably less than 50 nm such as 20 to 30 nm. Typical aspect ratios are within the range of 1 to 50 which clearly distinguishes those microdomain structures from carbon nanotubes that have aspect ratios in the range of 100 to 1,000.

[00016] Carbon disks and cones are carbon microdomain structures that are strongly dominant in the particulate carbon material present. Typically, the particulate carbon material comprises more than 90% by weight of carbon microdomain structures and up to about 10% by weight of common carbon black. The microdomain fraction of the particulate material normally comprises at least 10% by weight of carbon cones, preferably about 80% by weight of carbon disks and about 20% by weight of carbon cones. Additional microdomain or nanodomain structures such as nanotubes and fullerenes may also be present, but only in minute quantities.

[00017] The particulate carbon material present is produced by the so-called Carbon Black & Hydrogen Kvaerner Process, a plasma torch process, which is fully described in WO 98/42621. The production method can be summarized as a two-stage pyrolysis process in which a hydrocarbon feedstock is first conducted to a plasma zone and thereby subjected to a first smooth pyrolysis step in which the hydrocarbons are decomposed or cracked only partially to form polycyclic aromatic hydrocarbons (PAHs), before inserting PAHs into a second plasma zone sufficiently intense to complete the decomposition of hydrocarbons into elementary hydrogen and carbon.

[00018] US 6,476,154 addresses the use of the particulate microdomain carbon material present in diene-based elastomers to enhance the mechanical properties of rubber compositions. Applications of rubber compositions include tires, tracks and hoses. The thermal radioactive conductivity of the particulate carbon material is not mentioned or of any relevance to the intended applications referred to in US 6,476,154.

[00019] WO 2006/052142 refers to an electrically conductive composite material that comprises a non-conductive material by nature that has become conductive by carrying it with an electrical conductive charge consisting of the present particulate carbon material prepared by Kvaerner Carbon Black & Hydrogen Process. WO 2006/052142 also declares the charge and, consequently, the thermally conductive composite material, however, no evidence is provided.

[00020] In view of the teaching of WO 2006/052142 to add particulate carbon material to a non-conductive material to enhance thermal conductivity, it is quite surprising that particulate carbon material can be used for thermal insulation. The merit of the present inventors is the finding that the particulate microstructured carbon material has an exceptionally high extinction coefficient for infrared radiation, which makes it ideal for thermal insulation applications.

[00021] The specific extinction coefficient effective spectral e * A at a wavelength in the range of A = 1.4 μm to 35 μm is a measure for the attenuation of the thermal radiation that transmits the material. Extinction includes both an absorption and dispersion process within the material. The influence of anisotropic dispersion on radioactive transfer can be covered by scaling up to what are called effective amounts, marked with an is .. o ,, and u, i star. The spectral effective specific extinction coefficient e * A is determined by adding the spectral effective specific dispersion coefficient S * A to the spectral absorption coefficient aA.

[00022] The reciprocal of the product of the spectral effective extinction coefficient e '•• and the density p is the average free path L' of thermal radiation in the medium, that is, the path before dispersion or absorption occurs:

[00023] The spectral effective albedo (-'- 1 is the quotient between the spectral effective specific dispersion coefficient and the spectral effective specific extinction coefficient θ

[00024] The values of albedo •; between 0 and 1 (0 in the case of absorption only and 1 in the chaos of dispersion only).

[00025] A complete description of the optical-infrared properties is provided both by the extinction coefficient and by the albedo or the dispersion coefficient and the absorption coefficient. These four values are connected through Eq. (1) and Eq. 3.

[00026] In order to describe the total radiative thermal transport through the dispersion and absorption medium, the total specific extinction coefficient as a function of temperature and * (T) is obtained by integrating the spectral effective extinction coefficient and * A in all lengths of band A in the range A = 1.4 μm to 35 μm using the Rosseland weight function • '•:

[00027] where the Rosseland function is the partial derivative of the spectral intensity '=' vT: 'emitted by a blackbody at a given wavelength A and temperature T in relation to the total intensity ir'Tj at the same temperature:

em que T é a temperatura de amostra média e α = 5,67^10-8 W m-2K-4, a constante de Stefan-Boltzmann.[00028] The radiative conductivity can be calculated depending on the thickness of the sample if the total effective specific extinction coefficient is known:

where T is the average sample temperature and α = 5.67 ^ 10-8 W m-2K-4, the Stefan-Boltzmann constant.

: não depende da espessura de amostra.[00029] For thick optical samples 1 and e'-pd »D, Eq. (6) is reduced to:

: does not depend on the sample thickness.

[00030] In general, the total effective specific extinction coefficient e * for infrared radiation with x = 1.4 μm to 35 μm of the present particulate carbon material at 26.85 C (300 K) is within the range from from 1,200 to 1,700 m2 / kg, typically within the range from 1,290 to 1,640 m2 / kg. The parameters to calculate the total effective extinction coefficient and * of the particulate carbon material were obtained, as described in the example.

[00031] The infrared extinction of the present particulate microstructured carbon material is, in fact, far superior to that of carbon blacks and graphites known to have been used as thermal loads until then. It is a further fundamental advantage of the present invention that the specific particulate carbon material can be produced on an industrial scale at approximately the same magnitudes and production costs as ordinary carbon black.

[00032] Due to this unique IR extinguishing feature, the present particulate carbon material is useful in any application for thermal insulation both alone and, preferably, in combination with other material (s). Typically, these materials are thermally insulating and include both organic and inorganic thermal insulation materials. The addition of the present particulate carbon material to an insulation material significantly reduces the thermal conductivity through the composite and thereby enhances the insulating effect. Exemplary insulation materials that can be used in combination with the present particulate carbon material are both thermoplastic and thermoset polymeric materials; wood fiber materials, such as cork and wood straw; animal or vegetable fibers such as hemp, flax, straw; mineral and glass wool, sheet-shaped foamed glass; calcium silicate plaster sheets and plaster panels; fumed silica and mixtures of at least two of these materials. Examples of polymeric materials include vinyl polymers, preferably aromatic vinyl polymers, such as polystyrene, styrene copolymers with at least one copolymerizable monomer and polypropylene; as well as polyurethanes. In addition, mixtures of various polymers can be used. Thermally insulating polymeric materials, including those mentioned above, are typically present in the form of a foam cell both open and closed. The polymeric foams to be used together with the present particulate carbon material include, for example, expanded polystyrene (EPS), expanded styrene copolymers and at least one copolymerizable monomer, expanded polypropylene, extruded polystyrene (XPS) and polyurethane foam. In some embodiments, the polymeric foam comprises 1 to 10% by weight, preferably 1.5 to 8% by weight, more preferably 2 to 6% by weight of the present particulate carbon material, each of which is based on weight of the polymeric material.

[00033] Typically, the present particulate carbon material is used as an endogenous filler that is included / incorporated in a matrix material that is preferably a polymeric foam, as mentioned above. In some embodiments, the particulate carbon material is used as an aerobic filler (for example, in a matrix material that is preferably a polymeric foam, as mentioned above) together with at least one additional filler material that can be used. thermally insulating or not. Examples of filler materials for use with the present particulate carbon material include fumed silicas, such as Aerosil® R 812 (hydrophobic fumed silica post-treated with hexamethyldisilazane and available from Evonik Industries AG, Germany). A person skilled in the art knows well how to incorporate an aerobic charge in a polymeric foam and several methods are described in the literature, for example, in WO 2011/042800 which discloses several methods for preparing expanded and extruded expanded sheets of a thermoplastic polymer, of preferably polystyrene, loaded with an athermic charge.

[00034] In addition, the present particulate carbon material can be used in the vacuum insulated panel (VIPs) to further reduce thermal conductivity. It can be added to the material used as the support core, preferably it can be incorporated into the porous core material. The materials that can be employed for the core in combination with the present particulate carbon material include open cell polymer foams, such as polyurethane foams, microfiber materials, fumed silica and perlite.

[00035] Another application in which the present particulate carbon material can be used alone or in combination with another thermally insulating material is a filler for the insulation of high temperature furnaces.

EXAMPLES

[00036] Now, some embodiments of the present invention will be described in detail in the following examples.

MATERIALS:

[00037] All carbon black powders are commercially available from Orion Engineered Carbons GmbH, Hanau, Germany.

[00038] The powder specimen (example of the invention) and the 2 foams (examples of the invention 2 and 3) were investigated in order to obtain the total specific extinction coefficient e * at room temperature (26.85 C (300 K )).

MEASUREMENTS:

[00039] The samples were measured using a Vertex 70v Bruker Infrared Fourier Transform spectrometer in the wavelength range from 1.4 μm to 35 μm which is decisive for radiative thermal transport at room temperature. To measure the transmittance and directional-hemispheric spectral reflectance, thin films of dust specimens were chosen in supporting PE layers, which are transparent in the infrared wavelength range. The fine powder layers are sprayed onto the PE layer using a vacuum gauge. The preparation of homogeneous thin films is carried out with the commercial powder spreading system GALAI PD 10. A strong influx of air in an evacuated chamber turns the powder into de-agglomerated, partially electrically charged dust, which settles slowly on the support blade. and forms a reasonably stable specimen. Figure 2 shows the GALAI PD 10 vacuum powder spreading system; powder grains placed inside the cavity at the top of the evacuated container are sucked into the opening and settle on the PE blade. The thickness of the powder layer between 30 μm and 500 μm can be achieved by varying the amount of powder.

[00040] To measure the transmittance and spectral directional-hemispheric reflectance of the foams, several layers of each foam specimen were from the foam board. The diameter of the layers is 16 mm.

[00041] Then, the samples are placed in the opening of an integration sphere that is coupled to the spectrometer. Figure 3 shows the settings of the integration sphere to determine directional-hemispheric transmittance Tdh (on the left side) and the reflectance Rdh (on the right side) at normal room temperature at the surface. The sample is irradiated normal to the surface and the radiation reflected in the front-side hemisphere or transmitted in the rear-side hemisphere is measured for the transmittance or reflectance spectra, respectively. Several samples with different thicknesses were measured in order to consider possible homogeneities in the specimen and in order to guarantee a sufficiently satisfactory average measurement value. To calculate the spectral effective extinction coefficient e ■, the mass per area m "of each sample was also determined.

[00042] From the directional-hemispheric spectral transmittance and reflectance, the specific spectral effective extinction coefficient and • ■ and the spectral effective albedo of each specimen was calculated using a particular solution of the radiative transfer equation, the so-called three flow solution. The three-flow solution allows quantifying the radiative transfer by means of dispersion and absorption as well as determining the spectral dispersion and absorption coefficients of the investigated specimens.

[00043] Figure 4 shows the spectral specific absorption coefficient aA of particulate carbon material that comprises discs and cones (IE1) depending on wavelength A from 1.4 to 35 μm.

[00044] Figure 5 shows the spectral effective specific dispersion coefficient s •• of the particulate carbon material that comprises discs and cones (IE1) depending on wavelength A from 1.4 to 35 μm.

[00045] Figure 6 shows the specific effective dispersion coefficient spectral e * A of the particulate carbon material that comprises discs and cones (IE1) depending on the wavelength A from 1.4 to 35 μm.

[00046] Figure 7 shows the specific spectral absorption coefficient aA of IE2 (expanded polystyrene foam comprising 3% by weight of IE1) and IE3 (expanded polystyrene foam comprising 5% by weight of IE1) depending on the length A wave from 1.4 to 35 μm.

[00047] Figure 8 shows the spectral effective dispersion coefficient s * A of IE2 (expanded polystyrene foam comprising 3% by weight of IE1) and IE3 (expanded polystyrene foam comprising 5% by weight of IE1) depending on wavelength A from 1.4 to 35 μm.

[00048] Figure 9 shows the spectral and •• effective extinction coefficient of IE2 (expanded polystyrene foam comprising 3% by weight of IE1) and IE3 (expanded polystyrene foam comprising 5% by weight of IE1) depending on wavelength A from 1.4 to 35 μm.

[00049] From the spectral effective specific extinction coefficient and in the wavelength range between 1.4 μm and 35 μm, the total effective specific extinction coefficient at room temperature is calculated according to the equations in the description of the present application.

RESULTS:

[00050] In Table 1, the specific total extinction coefficient and * A of the specimens investigated at a temperature of 26.85 C (300 K) are reported. The total effective extinction coefficient e *, calculated from Eq. (4), can be determined with an accuracy of about 10% to 15%. TABLE 1 TOTAL EFFECTIVE SPECIFIC EXTINGUISHING COEFFICIENT AND *

[00051] Table 2 shows the total specific extinction coefficient e *, the radiative conductivity calculated according to Eq. (7) and the foam density p of the investigated foams IE2 and IE3 at a temperature T = 26 , 85 C (300 K). TABLE 2 PROPERTIES OF FOAM SAMPLES

[00052] It is evident from the results shown in Table 1 that the particulate microdomain carbon material comprising carbon discs and cones (IE1) has a specific total effective extinction coefficient significantly greater than * that of graphite used as fillers until then. Additionally, it is interesting to see in Table 2 that EPS foams loaded with the present particulate carbon material have exceptionally low thermal conductivities that are in a range normally achieved with vacuum insulated panels. This is especially noteworthy, since these low conductivities are achieved in EPS foam with relatively low densities of around 16 kg / m3. EPS foam discharged for insulation purposes needs to have densities of at least 30 kg / m3 due to the fact that lower densities cause a drastic increase in thermal conductivity.

Claims (14)

1. Use of a particulate carbon material, which comprises carbon particles in the shape of discs and hollow open cones, characterized by the fact that it is for thermal insulation. 2. Use according to claim 1, characterized by the fact that the hollow carbon cones have one or several of the following opening angles: 19.2 °, 38.9 °, 60 °, 83.6 ° and 112.9 °. 3. Use according to claim 1 or 2, characterized by the fact that the thickness of the carbon discs and the thickness of the hollow open carbon cone walls are less than 100 nm. 4. Use according to any one of claims 1 to 3, characterized in that the longest dimension of the carbon discs and hollow open carbon cones is less than 5 μm. 5. Use according to any one of claims 1 to 4, characterized by the fact that the particulate carbon material has a specific total extinction coefficient and * for IR radiation with Δ = 1.4 μm at 35 μm at 26 , 85 ° C (300 K), within the range from 1,200 to 1,700 m2 / kg. Use according to any one of claims 1 to 5, characterized in that the particulate carbon material is used in combination with at least one additional material, preferably a thermally insulating material. 7. Use, according to claim 6, characterized by the fact that said particulate carbon material is used as an aerobic charge. 8. Use, according to claim 7, characterized by the fact that the particulate carbon material is incorporated in a vacuum insulated (VIP) panel. Use according to claim 7, characterized by the fact that the particulate carbon material is incorporated into a matrix, which comprises at least one additional thermally insulating material, preferably a polymeric material. 10. Use according to claim 9, characterized by the fact that the thermally insulating material comprises at least one polymer selected from vinyl polymers, especially aromatic vinyl polymers, and polyurethanes. 11. Use according to claim 9 or 10, characterized by the fact that the thermally insulating material comprises a polymeric foam. 12. Use according to claim 11, characterized in that the polymeric foam comprises a thermoplastic or thermoset polymer. 13. Use according to claim 12, characterized in that the polymeric foam comprises at least one of expanded polystyrene, an expanded styrene copolymer and at least one copolymerizable monomer, expanded polypropylene, extruded polystyrene and polyurethane foam. 14. Use according to any of claims 9 to 13, characterized in that the particulate carbon material is used in conjunction with at least one additional filler material, such as fumed silica.

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